From 3574b567c486d264d680a37586436c3b5a8cb978 Mon Sep 17 00:00:00 2001
From: Philip McGrath <philip@philipmcgrath.com>
Date: Thu, 4 Mar 2021 04:11:50 -0500
Subject: [PATCH] patch rktio_process for "/bin/sh" on Guix

Racket provides the functions `system` and `process`,
which execute shell commands using `sh` (or `cmd` on Windows).
Racket assumes that `sh` can be found at "/bin/sh",
which is not necessarily true on Guix.

This patch adds a special case for "/bin/sh" to `rktio_process`,
the C function that implements the core of `system`, `process`,
and related Racket functions.

Guix should enable the special case by defining the C preprocessor
macro `GUIX_RKTIO_PATCH_BIN_SH` with the path to `sh` in the store.
If:

    1. The `GUIX_RKTIO_PATCH_BIN_SH` macro is defined; and

    2. `rktio_process` is called with the exact path "/bin/sh"; and

    3. The path specified by `GUIX_RKTIO_PATCH_BIN_SH` does exists;

then `rktio_process` will execute the file specified
by `GUIX_RKTIO_PATCH_BIN_SH` instead of "/bin/sh".

Compared to previous attempts to patch the Racket sources,
making this change at the C level is both:

    - More comprehensive: it catches all attempts to execute "/bin/sh",
      without having to track down the source of every occurance; and

    - Less intrusive: by guarding the special case with a C preprocessor
      conditional and a runtime check that the file in the store exists,
      we make it much less likely that it will "leak" out of Guix.
---
 racket/src/rktio/rktio_process.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/racket/src/rktio/rktio_process.c b/racket/src/rktio/rktio_process.c
index 89202436c0..465ebdd5c5 100644
--- a/racket/src/rktio/rktio_process.c
+++ b/racket/src/rktio/rktio_process.c
@@ -1224,12 +1224,14 @@ int rktio_process_allowed_flags(rktio_t *rktio)
 /*========================================================================*/
 
 rktio_process_result_t *rktio_process(rktio_t *rktio,
-                                      const char *command, int argc, rktio_const_string_t *argv,
+                                      /* PATCHED for Guix (next line) */
+                                      const char *_guix_orig_command, int argc, rktio_const_string_t *argv,
                                       rktio_fd_t *stdout_fd, rktio_fd_t *stdin_fd, rktio_fd_t *stderr_fd,
                                       rktio_process_t *group_proc,
                                       const char *current_directory, rktio_envvars_t *envvars,
                                       int flags)
 {
+  const char *command; /* PATCHED for Guix */
   rktio_process_result_t *result;
   intptr_t to_subprocess[2], from_subprocess[2], err_subprocess[2];
   int pid;
@@ -1255,6 +1257,23 @@ rktio_process_result_t *rktio_process(rktio_t *rktio,
   int i;
 #endif
 
+/* BEGIN PATCH for Guix */
+#if defined(GUIX_RKTIO_PATCH_BIN_SH)
+# define GUIX_AS_a_STR_HELPER(x) #x
+# define GUIX_AS_a_STR(x) GUIX_AS_a_STR_HELPER(x)
+  /* A level of indirection makes `#` work as needed: */
+  command =
+      ((0 == strcmp(_guix_orig_command, "/bin/sh"))
+       && rktio_file_exists(rktio, GUIX_AS_a_STR(GUIX_RKTIO_PATCH_BIN_SH)))
+      ? GUIX_AS_a_STR(GUIX_RKTIO_PATCH_BIN_SH)
+      : _guix_orig_command;
+# undef GUIX_AS_a_STR
+# undef GUIX_AS_a_STR_HELPER
+#else
+  command = _guix_orig_command;
+#endif
+/* END PATCH for Guix */
+
   /* avoid compiler warnings: */
   to_subprocess[0] = -1;
   to_subprocess[1] = -1;
-- 
2.21.1 (Apple Git-122.3)

